624 Ingenieurbau und Umwelttechnik
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A building's indoor climate is an essential input variable for a variety of building physics computational models, simulations, and analyses. Precise knowledge of the indoor climate is necessary to minimize the risk of mold or moisture damage and is required to ensure minimum heat insulation standards in buildings. Detailed data are especially necessary for the progressive application of transient calculations, for example, concerning thermal comfort or energy consumption. While the properties of building materials and the (local) outdoor climate are known, only rudimentary information about the dynamic indoor climate is available. Most existing information in the literature about indoor climate is fairly general and forgoes a differentiation between climatic region, occupancy profile, and the utilization of rooms. In this paper, we report on indoor climate measurements in naturally ventilated apartments over a period of 1 year. The measurement results complement the existing data to provide accurate indoor climate data in buildings. The measured values of indoor temperature and relative humidity serve to derive the dew point temperature and moisture load whereby dynamic time-dependent regression functions are determined for these parameters. The evaluations are carried out separately according to room use. The comparison of living rooms and bedrooms indicates a great influence of room use on the indoor climate in residential buildings. The determined indoor climate model can be used for the planning of buildings and simulations. The classification into living rooms and bedrooms makes it possible to take user behavior into account more realistically in building physics simulations. The minimum thermal insulation in residential buildings can also be checked and designed based on realistic data. The prediction interval describes the limits in which residential rooms are free of damage with a high probability. In this way, the indoor climate model describes an approach to examine and evaluate simulation results regarding condensation risk and mold damage in naturally ventilated rooms.
Tracking waterborne microplastic (MP) in urban areas is a challenging task because of the various sources and transport pathways involved. Since MP occurs in low concentrations in most wastewater and stormwater streams, large sample volumes need to be captured, prepared, and carefully analyzed. The recent research in urban areas focused mainly on MP emissions at wastewater treatment plants (WWTPs), as obvious entry points into receiving waters. However, important transport pathways under wet-weather conditions are yet not been investigated thoroughly. In addition, the lack of comprehensive and comparable sampling strategies complicated the attempts for a deeper understanding of occurrence and sources. The goal of this paper is to (i) introduce and describe sampling strategies for MP at different locations in a municipal catchment area under dry and wet-weather conditions, (ii) quantify MP emissions from the entire catchment and two other smaller ones within the bigger catchment, and (iii) compare the emissions under dry and wet-weather conditions. WWTP has a high removal rate of MP (>96%), with an estimated emission rate of 189 kg/a or 0.94 g/[population equivalents (PEQ · a)], and polyethylene (PE) as the most abundant MP. The specific dry-weather emissions at a subcatchment were ≈30 g/(PEQ · a) higher than in the influent of WWTP with 23 g/(PEQ · a). Specific wet-weather emissions from large sub-catchment with higher traffic and population densities were 1952 g/(ha · a) higher than the emissions from smaller catchment (796 g/[ha · a]) with less population and traffic. The results suggest that wet-weather transport pathways are likely responsible for 2–4 times more MP emissions into receiving waters compared to dry-weather ones due to tire abrasion entered from streets through gullies. However, more investigations of wet-weather MP need to be carried out considering additional catchment attributes and storm event characteristics.
The influence of the specimen size of ultra-high-performance fibre-reinforced concrete samples on the spatial distribution and orientation of the steel fibres is investigated. Specimens of varying size are produced by using the same protocol. They are imaged by micro-computed tomography to perform a statistical analysis of the spatial arrangement of the fibres. The tensile strength of the specimens is measured by tensile tests on subspecimens of equal size. The results are correlated to geometric characteristics of the fibre systems determined from the image data. Increasing the specimen size results in a larger variability of the local fibre geometry. This effect was most prominent when increasing the height of the specimens.
This DFG-funded research project aimed to gain a better understanding of the mechanisms of the W-Cl repair principle within the framework of fundamental investigations, to contribute to the creation of the necessary basis for a broader application of the repair principle in practice. The focus was on the development of a model to describe the chloride redistribution after the application of a system sealing surface protective coating. On the basis of Fick's second law of diffusion, a mathematical model with a self-contained analytical solution was developed, with the help of which the chloride redistribution after application of a system sealing surface protective coating can be calculated under the idealized assumption of complete water saturation of the concrete. Furthermore, the influence of the dehydration of the concrete, expected as a result of the application of the repair principle W-Cl, on the chloride redistribution was investigated. On the basis of laboratory tests and numerical simulations, material-specific reduction functions were developed to quantify the relationship between the chloride diffusion coefficient and the ambient humidity.
In this paper, the relationship between production parameters of ultra high performance fiber-reinforced concrete (UHPFRC) and the spatial distribution and orientation of the steel fibers is investigated. UHPFRC specimens with varying fiber diameter, fiber volume fraction, and rheology of the mixture are produced. Additionally, casting is performed from the side or the middle of the formwork. Imaging by micro computed tomography allows for a statistical analysis of the spatial arrangement of the fibers in the test specimens. The flexural behavior and the load capacity of the specimens are analyzed by four point bending tests. The results of the bending tests are well explained by characteristics of the fiber systems determined from the image data.
The increase of pluvial flooding has long been discussed to be a most probableoutcome of climate change. This has raised the question of necessary conse-quences in the design of urban drainage systems in order to secure adequateflood protection and resilience. Due to the uncertainties in future trends ofheavy rainfall events, the awareness of remaining risks of extreme pluvialflooding needs to be roused at responsible decision makers and the public aswell leading to the implementation of pluvial flood risk management (PFRM)concepts. The state of two core elements of PFRM in Germany are describedhere: flood hazard and risk evaluation and risk communication. In 2016 theguideline DWA-M 119 has been published to establish city-based PFRM con-cepts in specification of the European Flood Risk Management Directive(EU 2007). As core elements, the guidelines recommend a site-specific analysisand evaluation of flood hazards and potentials of flood damages to create floodhazard and flood risk maps. In the long run, PFRM needs to be established asa joint community effort and a requirement for more flood resilience. The riskcommunication within the administration and in the public requires a com-prehensible characterization and classification of heavy rainfall to illustrateevent extremity. The concept of a rainstorm severity index (RSI) instead of sta-tistical rainfall parameters appears to be promising to gain a better perceptionby affected citizens and non-hydrology-experts as well. A methodical approachis described to specify and assign site-specific rainfall depths within the sever-ity index scheme RSI12.This article is categorized under:
Engineering Water > Sustainable Engineering of Water
Engineering Water > Planning Water
Engineering Water > Methods
The dynamic behaviour of unsaturated sand rubber chips mixtures at various gravimetric contents is evaluated through an experimental study comprising resonant column tests in a fixed-free device. Chips were irregularly shaped with dimensions ranging from 5 to 14 mm. Three types of sand with different gradation have been considered. Relative density amounted to 0.5 for all specimens. Due to the large size of the chips, the diameter of the specimens had to be equal to 100 mm, which in turn required a re-calibration of the device assuming a frequency-dependent drive head inertia. The effects of confining stress, rubber chips content, and sand gradation on shear modulus and damping ratio are determined over wide ranges of the shear strain. At small strains, as known for sands, increasing the confining stress stiffens the mixtures. Increasing the rubber chips content reduces significantly the shear modulus and increases the damping ratio. At higher strains, increasing the confining stress or the rubber content flattens the reduction of the shear modulus with strain. Damping at high strains does not show any appreciable dependence on rubber content. Unloading–reloading sequences are used to assess shear modulus degradation and threshold strains. Finally, design equations are derived from the test results to predict the dynamic response of the composite material.
Der Wärmewende und der Abkehr von fossilen Energieträgern kommt gegenwärtig ein zentraler Stellenwert in der politischen Agenda zu. Die Herausforderung liegt insbesondere darin, Unabhängigkeit von Erdöl und Erdgas liefernden Staaten zu erreichen und klimaschädliche Technologien zu substituieren.
Chancen und Risiken aus Pflanzenverkohlung mittels Pyrolyseheizkesseln wurden im Hinblick auf deren Beitrag im Rahmen verschiedener Themen betrachtet werden. Hier könnte eine Kombination aus fossilfreier Nahwärmeversorgung, Nutzung nachwachsender regionaler Rohstoffe, Sequestrierung von atmosphärischem Kohlenstoff, Einflüsse auf die Qualität landwirtschaftlicher Böden durch Einbringen von Biokohle sinnvoll sein. Konkret wurde dies modellhaft anhand eines Biomasse-Nahwärmeprojekts einer kleinen Kommune in Oberbayern untersucht.
Im Rahmen dieser Arbeit werden Einflüsse dieser Technologie auf Treibhausgasemissionen in der Wärmewende, die Erfüllung von SDG-Indikatoren sowie Möglichkeiten, Pyrolysatoren ökonomisch kompetitiv zu gängigen Biomasseheizkesseln betreiben zu können, untersucht.
Particulate matter has been considered an indicator for the pollution of urban stormwater runoff for quite some time. There are only few studies that have investigated the contamination with organic micropollutants and metals both in the dis-solved and particulate phase as well as across different particle size classes. Yet, this distribution plays an important role in better understanding and optimising urban stormwater treatment measures. Therefore, this work aimed at assessing the composition of particulate matter in urban stormwater in terms of the physico-chemical properties (particle size distribution and organic content), as well as the occurrence of organic micropollutants and metals, their association to particulate matter and their removal from urban runoff. An intensive long term monitoring campaign at a centralised stormwater treatment facility of an industrial area was conducted. The stormwater runoff was sampled with large volume sampling tanks filled volume-proportional to the runoff at the two outlets of the facility. This allowed the determination of the event mean concentrations as well as the load-related removal efficiencies of the treatment facility for different parameters. Within each sample the concentrations of total suspended solids across different particle size fractions (< 63 µm, 63 – 125 µm, 125 – 250 µm, 250 – 2000 µm) were measured as well as their organic content. Furthermore, the concentrations and the phase distribution of 5 metals (Chromium, Copper, Zinc, Cadmium, Lead) and 29 organic micropollutants including polycyclic aromatic hydrocarbons, industrial chemicals (e.g. organophosphates, alkyphenols) and biocides were ana-lysed across different particle size fractions. In this study, over a period of almost 2.5 years, a total of 36 sampling events were recorded and investigated within two sampling periods (2015 – 2016 and 2017 – 2019) at the rainwater treatment facility in Freiburg Haid. The occurrence of organic micropollutants was determined in 22 of these events and the occurrence of metals in 17. The evaluation of the event mean concentration of total suspended solids showed that the fine fraction of the solids is of particular importance, as it showed an event mean concentration more than twice as high (34 mg \(L^{-1}\)) as the coarser particle fraction (14.9 mg \(L^{-1}\)). Regarding the occurrence of total suspended solids in terms of the transported solid load, the solids < 63 µm accounted for a mean proportion of 61 %, the fraction 63 – 125 µm for 13 %, the fraction 125 – 250 µm for 6 % and the fraction 250 – 2000 µm for 9 % of the total solid mass. In terms of the organic content of the solids, the results showed a clear increase of the organic content with increasing particle size (measured as loss on ignition).
As in the case of solids, the highest concentrations of the organic micropollutants and metals investigated were found in the particle size fraction < 63 µm. This fine fraction of the particles also accounted for the largest load of organic micropollutants and metals. Therefore, the particle loading with organic micropollutants or metals respectively the particle-bound micropollutant/metal concentration was calculated in this study. For most substances, a rather equal distribution over the smallest three particle size fractions was found. A certain correlation of the organic content with the occurrence of organic micropollutants and metals could be shown, therefore it can be assumed that the particle-bound concentration is certainly influenced by the organic content of the particulate matter. However, due to the fact that, among other things, the largest particle-bound pollutant loads are transported with particles < 63 µm, the fine fraction represents the relevant particle size in urban stormwater runoff. Regarding the total treatment efficiency (including sedimentation efficiency and volume retention), the investigated facility in this study was able to reduce the load of fine particles by only a quarter. The larger particle size classes were reduced by far more than half in most cases. If total suspended solids in its entire particle size range were used as a proxy to estimate the removal efficiency of metals and organic micropollutants, the efficiency would be overestimated and the actual pollutant load released into the environment would thus be underestimated. However, the investigation, weather the particle size fraction < 63 µm would be more suitable, showed that even for substances with a high tendency to adsorb onto particles (e.g. Cr, Cu, IND, GHI), the total treatment efficiency was still overestimated by the fine fraction.
Nitrogen removal from wastewater is increasingly important to protect natural water sources and has proven a challenge for wastewater treatment plants in different countries. Strict discharge norms for nitrogen components and unfavourable wastewater quality are among the main challenges observed.
An example WWTP (450,000 PECOD,120), representative of these challenges (i.e. strict discharge norm for NH4-N and TN, partially unfavourable wastewater composition for upstream denitrification) was modelled with the software SIMBA. The model was calibrated, and validated, using different statistical parameters. The model was used for dynamic simulation to test different operational and automation strategies, to improve nitrogen removal.
The tested strategies considered the bypass of primary clarifiers, changes in the anaerobic, anoxic, and aerobic reactors configuration, changes in the aeration system (DO setpoint, the inclusion of online sensors and different control approaches in the aeration loop), the adjustment of the internal recirculation rate, the implementation of intermittent denitrification, among others. The addition of an anaerobic digestion stage, considering the adjustment of the sludge age in the biological treatment and the treatment of the centrate (including nitrogen backload), was tested as well.
To evaluate the strategies' performance, an evaluation criteria chart was created to select the best strategies from an overall perspective, considering the improvements or deterioration in norm compliance, aeration requirements, pollutant emissions to the environment, and biogas production (if applicable).
The best overall results were obtained with strategies that aimed to improve the denitrification capacity (e.g. increase anoxic volume by reducing aerobic volume), adjusted the air requirements (e.g. inclusion of an NH4-N online measurement in the aeration control loop), and provided flexibility (e.g. intermittent denitrification). With the right combination of strategies, the norm compliance was significantly improved e.g. reduced from 31 to 4 in a year, as well as the emissions to the environment.
The inclusion of an anaerobic digestion stage for sewage sludge treatment challenges the nitrogen removal even further, but similar optimisation strategies, based on the same approach were able to improve norm compliance.
However, none of the combinations, with or without anaerobic digestion, achieved total norm compliance. Therefore, a different technology than A2/O, an SBR treatment stage was designed, providing increased operational flexibility. The A2/O system in the computer model was replaced by an SBR process. This showed the best results, based on the criteria previously defined, with total norm compliance.
Based on the learnings of the design, redesign, and strategies tested, a guideline for an integral optimisation of nitrogen removal was developed, based on six pillars, considering a detailed WWTP operational analysis, the use of dynamic simulation as a tool, the testing of known and simple optimization approaches, the definition of clear and objective evaluation criteria, the consideration of anaerobic digestion (and the backload) and finally the re-evaluation of the type of technology for biological wastewater treatment.